to start with I have a 79 bronco. Dana 60 front 14 bolt rear w/ 5.13 gears, 429,c6 & 205. I have replaced the dog house with a fiberglass tilt front end. the core support has been changed to aluminium 2x2 angle, angle also goes from the firewall to the core support with sheet aluminium hanging to keep mud off the engine compartment. Now as you can see I'm trying to get weight off the front of the truck. I have been throwng around the idea of moving the engine back, but I'm wondering if there is really an gain from moving the radiator to the rear. i know it transfers weight to the rear but it also adds weight by plumbing it to the rear and the weight of the coolant. and how far back do you run it. I was thinking above the rear axle to keep it away from me (the driver's compartment), and to put the weight where i want it. please let me know the pros & cons and any other ideas. Thank You

As far as weight goes your not moving enough to matter unless you use heavy tubing or something. These is a easier/lighter way further down.

Something that works on v8/BB wranglers that need the room is removing the tailgate and running a radiator in it's place. But basically you remove your tailgate build a radiator rack in the tailgates place. On the inside you build a heat shield and on the outside you have your fans. You can still have the tilt down tailgate if need be.
It works but there are quite a few downsides in your case.
It does require you to move your spare tire back which helps with the weight but takes away from your departure angle.
You have the issue of your back glass in your tailgate that would need to be addressed.
Your really not moving the radiator up much more then in the stock position so mud is still a issue.
The spare tire protects the fans/rad from most derbies. But if you need to make a sturdy(heavy) mount to ensure that if you/someone else slams into the tire mount it is not forced into the radiator.

The other alternative is moving the radiator inside the cab. The first safe place that comes to mind is behind the rear seat. Basically you would make a box and have cold air drawn in from the 3/4 panel and out through the 3/4 panel. By doing this you move the radiator to a safe place where mud can not get or affect it's cooling. By being inside a box and venting from/to the outside it also does not affect the heat inside. You could also incorporate a small vent door as part at the rear of the box to give you rear defrost.
This works great if you run the rear seat. If you do not run the rear seat it takes away from your cargo area. If you want more room you can move the box behind the driver/passenger seats using the same venting from/to the outside but now you have a box that will be seen by everyone all the time.

As far as lines go you can easily get exhaust tubing bent that will not weigh much. You can also go with hydraulic or high pressure hose relatively cheap used that will outlast your rig. I have used it in the past and it more then exceeds what your cooling system will require.

Now if you don't feel great about cutting holes into your body to place vents in it. Then there is nothing wrong with mounting the radiator under the hood. You could have the radiator mount to the one piece tilt piece and eliminate the front clip all together. Just use that hydraulic hose I talked about earlier and mount the hose low to keep everything from kinking and looking good. This would give a super clean look and also give you more working room while reducing weight. The only downside is that you will get more mud against the radiator then with the in cab method.

The one thing that you must do if you put a radiator inside is place it in side some type of a box so that if you do blow a hose suddenly the 200+- fluid does not cause burns like a mo fo to your passengers.

The rear seat box is what I would recommend unless you don't want to cut holes in your body then the clean look of a tilt one piece hood mounted radiator would be the second choice. The rear box is the safest, most efficient at guarding against mud, less noticeable, lets you move the battery(s) inside the box, and gives you a rear defrost option. If you want a option that you can change back to stock later on the tailgate method will work in that case as long as you keep all your old stock parts.